1. Field of the Invention
This invention relates generally to the recording and reproducing of information signals, such as, color video signals, and more particularly is directed to the reduction of interference due to cross-talk in the reproduction of relatively low frequency signals recorded in adjacent tracks which are very close together, for example, abutting or even in overlapping relation.
2. Description of the Prior Art
It is well known to record video signals on a magnetic tape or other record medium by scanning successive parallel tracks on the record medium with one or more transducers energized by the video signals. In effecting such recording of video signals, it has been the usual practice to provide guard bands or unrecorded gaps between the successive parallel tracks so that, when a transducer scans one of the tracks for reproducing the signals recorded therein, such transducer will not also reproduce crosstalk, that is, signals recorded in the adjacent tracks. However, the provision of guard bands between the successive parallel tracks reduces the recording density, that is, the amount of signal information recorded on a unit area of the record medium, and thus does not permit the efficient utilization of the record medium for the recording of video signals.
One effort made to minimize cross-talk while permitting an increase in the recording density has been to use two transducers having air gaps with different azimuth angles for recording and reproducing signals in the next adjacent or alternate tracks, respectively. This is relatively easy to do because apparatus for magnetically recording and/or reproducing video signals usually includes a rotary guide drum provided with two alternately operative transducers or heads which can have air gaps with different azimuth angles. The tape is wrapped helically about a portion of the perimeter of the guide drum and is moved longitudinally while the transducers or heads are rotated, thus causing the heads alternately to scan respective tracks on the tape for recording or reproducing signals therein. Each transducer or head, in the recording operation of the apparatus, effects magnetization of magnetic domains in the magnetic coating on the tape in what would appear to be, if such domains were visible, a series of parallel lines or stripes each having a length as great as the width of the track, and each having an orientation that corresponds to the azimuth angle of the gap of the respective transducer or head. In the reproducing or playback operation of the apparatus, each track is scanned by the transducer or head having its gap aligned with the parallel, but fictitious, lines of that track, from which it follows that the gap of the transducer or head scanning a track for reproducing the video signals recorded therein extends at an angle to the mentioned fictitious lines of the tracks next adjacent to the track being scanned. By reason of the foregoing, if a transducer or head, in scanning a track for reproducing the video signals recorded therein, overlaps an adjacent track or otherwise reproduces signals recorded in the latter, the well-known azimuth loss will result in attenuation of the cross-talk signal reproduced from the adjacent track.
When recording color video signals which include luminance and chrominance components, it is known to separate such components and then to frequency modulate a relatively high frequency carrier with the luminance component, while the chrominance component is frequency converted so as to have its frequency band shifted below the frequency band of the frequency modulated luminance component, whereupon the frequency modulated luminance component and the frequency converted chrominance component are combined to provide a composite video signal which is recorded in the successive parallel tracks. Since the previously mentioned azimuth loss is generally proportional to the frequency of the signals, the azimuth loss is relatively effective to decrease or eliminate interference due to cross-talk in respect to the relatively high frequency frequency-modulated luminance component. However, interference due to cross-talk from the relatively low frequency or frequency converted chrominance component is not sufficiently reduced by the use of transducers having different azimuth angles. Thus, when recording color video signals, it has been proposed, for example, as disclosed in detail in U.S. Pat. No. 4,007,482, issued Feb. 8, 1977 and having a common assignee herewith, to reduce or eliminate interference due to cross-talk in respect to a relatively low frequency signal recorded in adjacent tracks by recording the frequency converted component or other low frequency signal in such adjacent tracks with different first and second carriers, respectively, which may be distinguished from each other by their respective polarity characteristics. In a particular disclosed embodiment of the foregoing scheme, the first carrier for the frequency converted chrominance component has its phase unchanged throughout the recording of the video signals in a respective track, while the second carrier for the chrominance component recorded in the next adjacent track has its phase inverted or changed by 180.degree. for successive line intervals in the case of recording NTSC color video signals, or after each two line intervals in the case of recording PAL color video signals. When a head scans a particular track for reproducing the video signals recorded therein, the chrominance component of cross-talk signals from the tracks next adjacent to the scanned track can be conveniently suppressed or eliminated, for example, with the aid of a simple comb filter, by reason of the different polarity or phase characteristics of the carriers with which the chrominance component was recorded in the scanned track and in the tracks adjacent thereto, respectively.
Although the above described arrangement specifically disclosed in U.S. Pat. No. 4,007,482 effectively eliminates interference due to cross-talk in respect to the chrominance component while permitting a high recording density to be achieved by eliminating guard bands between the tracks and reducing the width of the latter, a few problems are encountered in the practical application thereof. More specifically, it is known that the second harmonic of the carrier frequency f.sub.c of the frequency converted chrominance component should be in interleaving relation with the frequency spectra of the luminance component which particularly appear at the horizontal or line frequency f.sub.H and multiples of the latter. Thus, in the existing arrangement, since the carrier of the frequency converted chrominance component recorded in every other track has its phase or polarity unchanged during the recording in each such track, it is necessary to provide the carriers of the frequency converted chrominance component with a frequency f.sub.c which is an odd multiple of 1/4f.sub.H, that is, f.sub.c =(2m-1)1/4f.sub.H or 2f.sub.c =(2m-1)1/2f.sub.H, in which m is a suitable whole number, for interleaving with the luminance component. By reason of the foregoing, when converting the chrominance component from its original carrier frequency f.sub.s to the relatively low carrier frequency f.sub.c for recording, and when reconverting the reproduced chrominance component back to its original or standard carrier frequency f.sub.s, it is necessary to provide a frequency converting and reconverting signal with a frequency, such as, for example, f.sub.s +44f.sub.H -1/4f.sub.H, which inconveniently includes a 1/4f.sub.H fraction.
Furthermore, when frequency reconverting the chrominance component of the video signals reproduced from the successive tracks, the circuit for providing the frequency reconverting signal includes an automatic phase control (APC) circuit for maintaining the proper phase relation of the frequency reconverting signal to the carrier of the reproduced chrominance component. However, in the case of the chrominance component recorded in the respective track with its carrier having the phase thereof inverted or changed by 180.degree. for successive line intervals or after each two line intervals, the automatic phase control circuit cannot follow or adjust for such large phase changes and it is desirable to provide the APC circuit with an additional phase identifying or detecting circuit.